Subduction zone thermal structure and mineralogy and their relationship to seismic wave reflections and conversions at the slab/mantle interface

Journal Article · Tue Jan 10 00:00:00 EST 1989 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB094iB01p00753· OSTI ID:5270234

Helffrich, G R; Stein, S; Wood, B J ^[1]

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1. Northwestern Univ., Evanston, IL (USA)

Seismological studies of the interface between downgoing slabs of subducted lithosphere and the overriding mantle provide constraints against which models of mantle and slab temperature and bulk composition can be tested. These studies, employing waves reflected and converted at the slab/mantle interface, suggest that a velocity contrast of 5-10% occurs over a distance of 10-20 km to depths of at least 350 km. The authors have investigated whether such sharp contrasts can result form thermal structure, compositional differences, phase changes, or other effects such as preferred mineral orientation. Using a mantle and slab temperature model, a petrologic model of mantle and slab mineralogy, and a data base of elastic properties of mantle and slab phrases, theoretical seismic velocities were calculated and compared with the observed velocity contrast and boundary thickness constraints. At 9.6 GPa and 1000C (conditions modeled at the slab/mantle interface at {approximately}280-km depth), cooler temperatures in the slab interior produce, at constant composition, only approximately a 1.75% V{sub p} increase into the slab in any of the peridotitic and eclogitic mineralogies investigated. Variation in V{sub p} among the different bulk compositions is only approximately 0.5%. These contrasts are substantially lower than those obtained from the seismological studies and indicate that temperature and bulk compositional differences between mantle and slab are inadequate to cause the observed velocity contrasts. They propose that phase transformations in mantle and slab mineralogies, notably elevation of the olivine-spinel phase change normally occurring at 400-km depth, are important factors in these sharp contrasts. Other contributing effects may include preferential mineral orientation near the slab surface and, at shallower depths, the presence of partial melt or hydrous fluid evolved from dehydration reactions along the interface.

• OSTI ID: 5270234
• Journal Information: Journal of Geophysical Research; (United States), Vol. 94:B1; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
SUBDUCTION ZONES
MINERALOGY
SEISMIC SURVEYS
TEMPERATURE GRADIENTS
BOUNDARY CONDITIONS
CONTINENTAL CRUST
DATA ANALYSIS
DEPTH
EARTH MANTLE
ELASTICITY
GEOLOGIC MODELS
INTERFACES
OLIVINE
ORIENTATION
PETROLOGY
PHASE TRANSFORMATIONS
PLATE TECTONICS
ROCK MECHANICS
SEISMIC WAVES
SPINELS
THICKNESS
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
DIMENSIONS
EARTH CRUST
GEOLOGY
GEOPHYSICAL SURVEYS
IRON COMPOUNDS
IRON SILICATES
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
MAGNESIUM SILICATES
MECHANICAL PROPERTIES
MECHANICS
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SURVEYS
TECTONICS
TENSILE PROPERTIES
TRANSITION ELEMENT COMPOUNDS
580000* - Geosciences